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Blocked Port 25? .. Mail on a Non-Standard Port

When I first began playing with linux so many years ago I found it fun to send mail from my Windows machine (located on the floor right next to my linux box) to sendmail, which would then have to send it back through my gateway, which was the Windows machine! This was merely amusing and not very useful, but it did teach me much about mail protocols and how dial-up PPP interacts with an ISP. This is how it works: Your email program, Eudora for example, has a setting for an SMTP server. When you send an email message a connection is created to that SMTP server on port 25, the message is transferred and you disconnect. From there, the SMTP server looks up the MX record for the destination host of the email (the part of the email address after the '@' sign) and connects to that SMTP server, also on port 25. The mail is transferred to this new server and if this is the destination for the email message, it is delivered to the appropriate user.

Now, years away from my neophyte tinkering, I administer multiple mail servers and run one at home. But here's the rub: Cox cable, my home Internet provider, blocks port 25, the default SMTP port (used for incoming and outgoing mail.) This may sound like they are doing something mean, but their intentions are pure. Many home users run misconfigured mail servers (often unknowingly) that transport spam and viruses. When the ISP blocks port 25, these dangerous transports are effectively cut off from the Internet. But what about we informed users who just want some professional facilities at home? What about us?!

To the lament of the computing community No-IP.com raised a benevolent ear and came up with Reflector. Reflector effectively bypasses the protective impediment your ISP has created returning liberty to the seekers of knowledge (and those who just want all of their ports.) By configuring your home mail server to use a non-standard port and using reflector, the outside world will be able to deliver mail to your server. With Reflector the mail delivery process changes at the point where the SMTP server looks up the MX record for the destination host of the email. The lookup returns No-IP's mail server. The message is delivered to No-IP and No-IP sends it on to your mail server, but connects on your non-standard port thereby thwarting your ISP's block. Not only that, but Reflector also gives you the added benefit of Backup MX, that is, if your mail server goes down, No-IP spools your mail until your mail server comes back up! Here's how to set up Reflector:

  1. Configure your mail server to use a port other than 25. This should be a high numbered port to avoid conflicts with other well-known ports. I prefer port 9925. All decent mail servers can do this, check your documentation.
  2. Sign up for No-IP's Reflector. The set up for Reflector is painless and only takes a matter of seconds:
    1. Log in to No-IP.com (create an account if you don't have one, its free) and click on Add Mail Service under No-IP Mail on the left.
    2. Enter the domain you would like reflected. Choose Mail Reflector on the next page and activate the service.
    3. Go to Manage Mail under No-IP Mail (right below Add Mail Service.) You will see your domain listed with type: Reflector and status: Active. Under Action choose Modify
    4. Enter the non-standard port number you configured on your mail server. In the mail server text field enter the fully qualified domain name of your mail server (e.g. mail.mydomain.com) or the IP address. No-IP will verify the port, so be sure your mail server is running.
    5. If No-IP was able to verify your server, its time to change your MX record. If not, check your mail server and its documentation and try until it verifies.
    6. If the domain of your mail server is managed by No-IP, go to the manage hosts section. Choose modify on the domain to which your mail server is configured. This would be whatever comes after the '@' in the email address. At the bottom of the page under Mail Options enter mail1.no-ip.com for priority 5 and mail2.no-ip.com for priority 10.
    7. If your domain is not managed by No-IP.com, you will have to change your MX record at your registrar's or DNS providers site. The settings should be mail1.no-ip.com for priority 5 (i.e. primary) and mail2.no-ip.com for priority 10 (i.e. backup).
    8. You are now set up on No-IP.com. The port number changes are immediate, but the changes to the MX record can take up to 5 minutes. Time to test!
  3. Test the configuration. From a computer other than your mail server, send an email to an account residing on your mail server. Delivery should only be taking a few minutes depending on your ISP's SMTP server. You should receive the email without complication. In the header of the message you will see the message relayed through a No-IP.com or Vitalwerks.com mail server (for example, "Received: from goodyear.vitalwerks.com [63.210.163.179] by splizzle with Microsoft SMTPSVC(6.0.2600.1); Fri, 9 Aug 2002 14:21:06 -0700".) If you have something like this, congratulations, everything is working! If not, check over each part of your configuration and use nslookup to check the MX record for you domain.

Now that you have Reflector set up you can add many things to your home mail server such as IMAP, Mail Backup, Web Mail, or logging. You can even set up accounts for yoru friends! Reflector is also perfect for businesses that use a shared DSL line or cable hook up. Demand full control over your email!

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